With SourceOffSite 5, the File View can be sorted with multiple columns. Simple hold down "SHIFT" while clicking column headers to "add" the columns to the sort list. To reverse a sort order, simply click the column a second time.

The sort list works in a LIFO/stack manner, so the last column clicked is the first column in the sort. Another way to think about this is to add columns from LEAST significance to MOST significance in your sort. Also when reversing the order, create your reverse "sort columns" by placing a column in descending order first (holding down shift if this is not the LEAST significant column), and then add other columns by SHIFT+CLICK ing the other headers.